Fifty years ago, Skopje, the capital of Macedonia, was hit by a huge earthquake that flattened the city. Two years later, Japanese architect Kenzo Tange won a competition to design the new city center. And his influence on the city's retrofuturistic look is still apparent decades later.

The second life of Olympic structures is a challenge to manage for any host city. But none, perhaps, offer as stark an image as Sarajevo's battle-scarred Olympic buildings. Eight years after the 1984 winter games, the Bosnian War left the city with buildings full of bullet holes, ski slopes dotted with land mines, and…

In the Seventies and Eighties, Yugoslavian science magazine Galaksija pumped out dozens of mind-blowingly weird covers that could easily be mistaken for prog rock LPs. Here's but a sampling of the many triptacular designs that hit Balkan newstands several decades ago.

Remember Linda Ferrari's photographs of Bulgarian Socialist memorials? Jan Kempenaer has shot similar monuments in former Yugoslavia. Many of these Socialist sculptures have been weathered by the elements, making them look like the remnants of some strange extraterrestrial civilization.

Even if you've been to the Catacombs of Paris or have gone spelunking in Brooklyn's abandoned subway lines, there's still a wealth of underground places to be explored. Here are some of the world's less welcoming manmade tunnels and grottos.